Transfer device and route addition method

ABSTRACT

Provided are a redundant route calculator that calculates, on the basis of first topology information on a network made up of a plurality of transfer devices, a plurality of shortest routes from a first transfer device to a second transfer device among the plurality of transfer devices, and generates redundant route information; a forwarding database that stores the redundant route information; and a single point-of-failure detector that detects a single point of failure on the basis of the redundant route information and generates second topology information obtained by removing the single point of failure from the first topology information. On the basis of the second topology information, the redundant route calculator calculates an additional route candidate from the first transfer device to the second transfer device. The single point-of-failure detector decides the additional route to register in the forwarding database.

FIELD

The present invention relates to a transfer device and a route additionmethod that transfer a frame in a mesh network.

BACKGROUND

There is a mesh network as one of network configurations. In the meshnetwork, redundancy of communication routes, that is, paths are easilyimplemented by adopting a form in which respective communication devicesare interconnected like a mesh. Shortest path bridging (SPB) is aprotocol that implements control of redundant paths in the mesh network(Non Patent Literature 1). The SPB is a technology that configures anequal cost multi-path (ECMP) to enable high-speed path switching at theoccurrence of a failure, redundant path configuration, trafficdistribution, and the like.

CITATION LIST Non Patent Literature

Non Patent Literature 1: Institute of Electrical and ElectronicsEngineers (IEEE) Std 802.1aq-2012

SUMMARY Technical Problem

However, according to the conventional technology mentioned above, inthe mesh network, a plurality of paths can be set between twocommunication devices to achieve redundancy, but a single point offailure (SPOF) is sometimes formed on the set redundant path. There is adifficulty that communication between the two communication devices isinterrupted in spite of a redundant path being set therebetween when afailure occurs in the communication device or the communication passagecorresponding to the SPOF.

The present invention has been made in view of the above situation andhas as its object to obtain a transfer device capable of improving thereliability of communication in a mesh network.

Solution to Problem

In order to solve the above problems and attain the object, the transferdevice of the present invention includes: a redundant route calculatorthat, on the basis of first topology information that is topologyinformation on a network made up of a plurality of transfer devices,calculates a plurality of shortest routes from a first transfer deviceto a second transfer device among the plurality of transfer devices, andgenerates redundant route information that is information on theplurality of shortest routes; an information storage that stores theredundant route information; and a single point-of-failure detector thatdetects a single point of failure on the basis of the redundant routeinformation and generates second topology information that is topologyinformation obtained by removing the single point of failure from thefirst topology information. On the basis of the second topologyinformation, the redundant route calculator calculates a candidate of anadditional route to be added as a route from the first transfer deviceto the second transfer device, and generates additional route candidateinformation that is information on the candidate of the additionalroute. The single point-of-failure detector decides the additional routeon the basis of the additional route candidate information, andgenerates additional route information that is information on theadditional route, to register the generated additional route informationin the information storage.

Advantageous Effects of Invention

The transfer device according to the present invention has the effect ofbeing able to improve the reliability of communication in a meshnetwork.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a configuration example of a meshnetwork.

FIG. 2 is a block diagram illustrating a configuration example of atransfer device.

FIG. 3 is a flowchart illustrating an example of the operation of aroute calculation process of the transfer device.

FIG. 4 is a diagram illustrating an example of a mesh network forexplaining a process in which a single point-of-failure detector detectsa single point of failure.

FIG. 5 is a diagram illustrating an example of the mesh network obtainedin such a manner that the single point-of-failure detector has detecteda single point of failure in the mesh network illustrated in FIG. 4 andthe single point of failure has been removed.

FIG. 6 is a diagram illustrating another example of a mesh network forexplaining a process in which the single point-of-failure detectordetects a single point of failure.

FIG. 7 is a diagram illustrating an example of the mesh network obtainedin such a manner that the single point-of-failure detector has detecteda single of point failure in the mesh network illustrated in FIG. 6 andthe single point of failure has been removed.

FIG. 8 is a diagram illustrating a hardware configuration example of thetransfer device.

FIG. 9 is a diagram illustrating another hardware configuration exampleof the transfer device.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a transfer device and a route addition method according toembodiments of the present invention will be described in detail withreference to the drawings. Note that this invention is not limited bythese embodiments.

Embodiment

FIG. 1 is a diagram illustrating a configuration example of a meshnetwork 30 according to an embodiment of the present invention. The meshnetwork 30 is a network made up of transfer devices 10-1 to 10-6 thattransfer frames. In addition, terminal devices 20-1 to 20-7 to serve asa transmission source of a frame or a destination of a frame areconnected to the mesh network 30. In the following description, when thetransfer devices 10-1 to 10-6 are not distinguished, the transferdevices 10-1 to 10-6 are referred to as transfer devices 10 in somecases. Likewise, when the terminal devices 20-1 to 20-7 are notdistinguished, the terminal devices 20-1 to 20-7 are referred to asterminal devices 20 in some cases.

The transfer device 10 is a switch device that can be connected to oneor more other transfer devices 10 and one or more terminal devices 20.Each transfer device 10 exchanges connection information with anothertransfer device 10 constituting the mesh network 30 and generatestopology information on the mesh network 30 from connection informationcollected from the other transfer devices 10 to store. The connectioninformation is information about the transfer device 10 to which anothertransfer device 10 is connected. The topology information on the meshnetwork 30 is taken as first topology information. In addition, eachtransfer device 10 decides a communication route leading to each of theother transfer devices 10, that is, the route for communicating witheach of the other transfer devices 10, by SPB. In the followingdescription, the route is referred to as a path in some cases.

The terminal device 20 is connectable to one transfer device 10. Theterminal device 20 communicates with, that is, transmits and receivesframes to and from another terminal device 20 via one or more transferdevices 10. In FIG. 1, the connection relationship between each transferdevice 10 and each terminal device 20 is indicated by a solid line andthe solid line represents a communication passage as well. In thefollowing description, the communication passage between adjacenttransfer devices 10 is referred to as a link in some cases.

The configuration of the transfer device 10 will be described. FIG. 2 isa block diagram illustrating a configuration example of the transferdevice 10 according to the present embodiment. The transfer device 10includes a link state database 11, a redundant route calculator 2, aforwarding database 13, a single point-of-failure detector 14, and avirtual link state database 15. The redundant route calculator 12includes a shortest route calculator 121 and a tie breaker 122. Notethat FIG. 2 depicts the main part of the transfer device 10 related tothe characteristic operation of the present embodiment, specifically,functional blocks necessary for setting the route for communicating withanother transfer device 10, and illustration of other functional blocksincluded in the general transfer device is omitted in FIG. 2.

The link state database 11 is a first information storage. The linkstate database 11 stores the first topology information, which istopology information on the mesh network 30 made up of the plurality oftransfer devices 10. The first topology information includes informationon the connection relationship between the transfer devices 10 and alink cost. The link cost is, for example, the bandwidth of each link.

On the basis of the first topology information held by the link statedatabase 11, the redundant route calculator 12 calculates one or moreshortest paths, that is, shortest routes for every combination of pairof the plurality of transfer devices 10 constituting the mesh network30. The redundant route calculator 12 uses the SPB when calculating theshortest route. In the redundant route calculator 12, the SPB isimplemented by operations of the shortest route calculator 121 and thetie breaker 122. Note that, in the case of the combination of thetransfer devices 10 adjacent to each other in the mesh network 30, thecombination of the adjacent transfer devices 10 has a single shortestroute.

On the basis of the first topology information held by the link statedatabase 11, the shortest route calculator 121 of the redundant routecalculator 12 calculates the shortest route between each pair of thetransfer devices 10, with respect to all the possible combinations ofpairs of the plurality of transfer devices 10 constituting the meshnetwork 30. For example, the shortest route calculator 121 uses, as analgorithm for calculating the shortest route, the Dijkstra's Algorithmdescribed in “A Note on Two Problems in Connexion with Graphs(“Numerische Mathematik” Volume 1, 1959, p. 269-271)”. The shortestroute calculator 121 notifies the tie breaker 122 of selectioninformation, which is information on the link cost of each routecalculated for each pair of the transfer devices 10, and the like.

In each pair of the transfer devices 10, when there is a plurality ofshortest routes from the transfer device 10 at the start point to thetransfer device 10 at the end point, the tie breaker 122 of theredundant route calculator 12 selects one of the plurality of shortestroutes by a tie-breaking algorithm, on the basis of the selectioninformation from the shortest route calculator 121. The transfer device10 at the start point is referred to as a first transfer device and thetransfer device 10 at the end point is referred to as a second transferdevice in some cases. The tie breaker 122 notifies the shortest routecalculator 121 of the selection result.

On the basis of the selection result from the tie breaker 122, theshortest route calculator 121 generates redundant route information,which is information on the shortest route, and registers the generatedredundant route information in the forwarding database 13. For example,when there is a plurality of shortest routes, the shortest routecalculator 121 generates the redundant route information on the shortestroute selected by the tie breaker 122 as one piece of the redundantroute information. Note that, for convenience of explanation, even ifonly one shortest route is obtained as a result of calculation by theredundant route calculator 12, information on the shortest route to beregistered in the forwarding database 13 by the shortest routecalculator 121 and information on the shortest route to be output to thesingle point-of-failure detector 14 by the shortest route calculator 121are regarded as the redundant route information. Details of theredundant route calculation procedure by the shortest route calculator121 and the tie breaker 122 of the redundant route calculator 12 aredescribed in Non Patent Literature 1.

The forwarding database 13 is a second information storage. Theforwarding database 13 is a database generally equipped in a devicehaving a frame transfer function and corresponds to, for example, avirtual local area network (VLAN) table. The forwarding database 13stores the redundant route information, which is information on aplurality of shortest routes calculated by the redundant routecalculator 12 and stores information indicating which adjacent transferdevice 10 the frame received by the transfer device 10 should betransferred to. The forwarding database 13 is simply referred to as aninformation storage in some cases.

On the basis of the redundant route information calculated by theredundant route calculator 12, the single point-of-failure detector 14determines whether there is a transfer device 10 or a link serving as asingle point of failure on the route between two transfer devices 10.The single point of failure means a place where, although there is aplurality of shortest routes indicated by the redundant routeinformation, if a failure occurs in a certain transfer device 10 or acertain link, a failure occurs in all the shortest routes andconsequently a communication failure is brought about between the pairof transfer devices 10 according to the redundant route information.There are both possibilities that the transfer device 10 is applicableand the link is applicable as a single point of failure. When a singlepoint of failure has been detected, that is, when there is a singlepoint of failure, the single point-of-failure detector 14 generates thesecond topology information, which is the topology information obtainedby removing the single point of failure from the first topologyinformation held in the link state database 11, that is, topologyinformation about a network obtained by removing the transfer device 10or the link serving as the single point of failure from the mesh network30, and registers the generated second topology information in thevirtual link state database 15. In this manner, the singlepoint-of-failure detector 14 generates the second topology informationon the basis of the redundant route information and the first topologyinformation. Details of the operation of the single point-of-failuredetector 14 will be described later.

The virtual link state database 15 is a third information storage. Thetype of data held in the virtual link state database 15 is similar tothat of the link state database 11, but the content of data held in thevirtual link state database 15 is the second topology informationgenerated by the single point-of-failure detector 14 as described above.

Subsequently, an operation of the transfer device 10 for calculating aroute that does not form a single point of failure, that is, a routecalculation process will be described. FIG. 3 is a flowchartillustrating an example of the operation of the route calculationprocess of the transfer device 10 according to the present embodiment.The flowchart illustrated in FIG. 3 specifically illustrates an exampleof the operation until the transfer device 10 registers, in theforwarding database 13, route information that does not form a singlepoint of failure, taking the first topology information held in the linkstate database 11 into account. In a case where the first topologyinformation held by the link state database 11 is changed due to achange in the configuration of the mesh network, the transfer device 10executes the operation of the route calculation process in accordancewith the flowchart illustrated in FIG. 3 when a predetermined conditionis satisfied such as when receiving an instruction from an externalnetwork administrator. Note that the transfer device 10 performs theprocess of the flowchart illustrated in FIG. 3 for each of allcombinations of pairs of the plurality of transfer devices 10constituting the mesh network 30.

First, in the transfer device 10, on the basis of the first topologyinformation held in the link state database 11, the redundant routecalculator 12 chooses a certain pair of the transfer devices 10constituting the mesh network as a target and calculates one or moreshortest routes between the pair of the transfer devices 10 (step S11).As described earlier, in the case of the combination of the transferdevices 10 adjacent to each other in the mesh network, one shortestroute is found. Accordingly, including such a case, the process in stepS11 is also regarded as a process in which the redundant routecalculator 12 calculates the redundant route. The redundant routecalculator 12 registers the redundant route information, which isinformation on the calculated redundant route, in the forwardingdatabase 13 (step S12). In addition, the redundant route calculator 12outputs the redundant route information to the single point-of-failuredetector 14. Steps S11 and S12 constitute a first calculation step.

On the basis of the redundant route information received from theredundant route calculator 12, the single point-of-failure detector 14determines whether there is a single point of failure on the routebetween the two transfer devices 10 (step S13). FIG. 4 is a diagramillustrating an example of a mesh network 31 for explaining a process inwhich the single point-of-failure detector 14 according to the presentembodiment detects a single point of failure. The mesh network 31 isconstituted by transfer devices 10-1 to 10-11. For example, when theshortest route from the transfer device 10-1 to the transfer device10-11 is calculated by the SPB, the single point-of-failure detector 14detects the transfer device 10-5 as a single point of failure. Notethat, in the example in FIG. 4, the transfer device 10-1 serves as thefirst transfer device and the transfer device 10-11 serves as the secondtransfer device.

Specifically, in the mesh network 31 illustrated in FIG. 4, thefollowing four routes in total are given as the shortest route from thetransfer device 10-1 to the transfer device 10-11: a route indicated by“10-1>10-2>10-5>10-9>10-11” leading to the transfer device 10-11 fromthe transfer device 10-1 by way of the transfer devices 10-2, 10-5, and10-9 in this order; a route indicated by “10-1>10-2>10-5>10-10>10-11”leading to the transfer device 10-11 from the transfer device 10-1 byway of the transfer devices 10-2, 10-5, and 10-10 in this order; a routeindicated by “10-1>10-3>10-5>10-9 >10-11” leading to the transfer device10-11 from the transfer device 10-1 by way of the transfer devices 10-3,10-5, and 10-9 in this order; and a route indicated by“10-1>10-3>10-5>10-10>10-11” leading to the transfer device 10-11 fromthe transfer device 10-1 by way of the transfer devices 10-3, 10-5, and10-10 in this order.

By examining route information obtained by excluding the transfer device10-1 as the start point and the transfer device 10-11 as the end pointfrom the route information on these four routes, that is, pieces ofinformation “10-2>10-5>10-9”, “10-2>10-5>10-10”, “10-3>10-5>10-9”, and“10-3>10-5>10-10”, it can be seen that the transfer device 10 includedin all the pieces of route information on the four routes is thetransfer device 10-5. The single point-of-failure detector 14 detectsthe transfer device 10-5 as a single point of failure by the abovemethod.

When a single point of failure has been detected, that is, when there isa single point of failure (step S13: Yes), the single point-of-failuredetector 14 generates the second topology information obtained byremoving the single point of failure from the first topology informationheld in the link state database 11 and registers the generated secondtopology information in the virtual link state database 15 (step S14).For example, in the mesh network 31 illustrated in FIG. 4, when thesingle point of failure formed on the shortest route from the transferdevice 10-1 to the transfer device 10-11 is removed, the topologyillustrated in FIG. 5 is obtained. FIG. 5 is a diagram illustrating anexample of the mesh network 31 obtained in such a manner that the singlepoint-of-failure detector 14 according to the present embodiment hasdetected a single point of failure in the mesh network 31 illustrated inFIG. 4 and the single point of failure has been removed. The secondtopology information held in the virtual link state database 15 is in astate in which the transfer device 10-5 has been removed from the firsttopology information held in the link state database 11.

Note that, when a single point of failure has not been detected, thatis, there is no single point of failure (step S13: No), the transferdevice 10 terminates the process. Steps S13 and S14 constitute a firstdetection step.

On the basis of the second topology information held in the virtual linkstate database 15, the redundant route calculator 12 chooses the samepair of transfer devices 10 as in step S11 as a target and calculatesthe shortest route between the pair of transfer devices 10 (step S15).Furthermore, the redundant route calculator 12 determines whether thereis a shortest route, that is, whether there is a route linking thetransfer device at the start point to the transfer device at the endpoint (step S16). This is because there is a case where the mesh network31 is separated by removing a single point of failure.

When calculating as many shortest routes as possible on the basis of thesecond topology information obtained by removing the single point offailure formed on the shortest route from the transfer device 10-1 tothe transfer device 10-11, that is, the transfer device 10-5 from themesh network 31 illustrated in FIG. 4, the redundant route calculator 12calculates two shortest routes indicated by arrows in FIG. 5.

FIG. 6 is a diagram illustrating an example of a mesh network 32 forexplaining a process in which the single point-of-failure detector 14according to the present embodiment detects a single point of failure.In addition, FIG. 7 is a diagram illustrating an example of the meshnetwork 32 obtained in such a manner that the single point-of-failuredetector 14 according to the present embodiment has detected a singlepoint of failure in the mesh network 32 illustrated in FIG. 6 and thesingle point of failure has been removed. The mesh network 32illustrated in FIG. 6 has the same arrangement of the transfer devices10 as the arrangement in the mesh network 31 illustrate in FIG. 4, buthas different wiring of some communication passages between the transferdevices 10.

In the mesh network 32 illustrated in FIG. 6, the single point offailure on the shortest route from the transfer device 10-1 to thetransfer device 10-11 is the transfer device 10-5. When the singlepoint-of-failure detector 14 removes the transfer device 10-5 from themesh network 32 in step S14, the mesh network 32 is separated asillustrated in FIG. 7. In this case, a route linking the transfer device10-1 to transfer device 10-11 no longer exists. In consideration of sucha case, the redundant route calculator 12 determines in step S16 whetherthere is a shortest route, that is, there is a route linking thetransfer device 10-1 at the start point to the transfer device 10-11 atthe end point.

When there is a route linking the transfer device 10-1 at the startpoint to the transfer device 10-11 at the end point in the calculationof the shortest route (step S16: Yes), the redundant route calculator 12assigns the calculated shortest route as an additional route candidatethat is a candidate to be added to the forwarding database 13, andgenerates additional route candidate information, which is informationon the additional route candidate, to output to the singlepoint-of-failure detector 14. When there is no route linking thetransfer device 10-1 at the start point to the transfer device 10-11 atthe end point (step S16: No), the redundant route calculator 12 notifiesthe single point-of-failure detector 14 of the fact that the shortestroute could not be calculated. Steps S15 and S16 constitute a secondcalculation step.

On the basis of the additional route candidate information, the singlepoint-of-failure detector 14 determines whether there is a single pointof failure on the route between two transfer devices 10 (step S17). Themethod of determining whether there is a single point of failure by thesingle point-of-failure detector 14 in step S17 is similar to the methodin the case of step S13. When the single point of failure has not beendetected, that is, when there is no single point of failure (step S17:No), the single point-of-failure detector 14 stores an additional routecandidate having the shortest route length among the additional routecandidates, and the distance of that additional route candidate. Thesingle point-of-failure detector 14 stores the shortest additional routecandidate and the distance thereof for each pair of the transfer devices10 at the start point and the transfer device 10 at the end point.Taking the mesh network 31 illustrated in FIG. 4 as an example, thesingle point-of-failure detector 14 separately stores information on theshortest additional route candidate from the transfer device 10-1 to thetransfer device 10-11 and the distance thereof (hereinafter referred toas information 1) and information on the shortest additional routecandidate from the transfer device 10-11 to the transfer device 10-1 andthe distance thereof (hereinafter referred to as information 2). Thesingle point-of-failure detector 14 does not compare the information 1with the information 2.

The single point-of-failure detector 14 compares the distance of thenewly stored additional route candidate with the distance of the storedadditional route candidate. When the distance of the newly storedadditional route candidate is shorter than the distance of the storedadditional route candidate, that is, when the newly stored additionalroute candidate is the shortest among the additional route candidates(step S18: Yes), the single point-of-failure detector 14 stores thenewly stored additional route candidate as the latest additional routecandidate and updates the additional route candidate (step S19). Notethat the single point-of-failure detector 14 may carry out step S19 byskipping step S18 when there is no stored additional route candidate,that is, at the time of the initial operation.

When receiving a notification from the redundant route calculator 12indicating that there is no route linking the transfer device 10-1 atthe start point to the transfer device 10-11 at f the end point (stepS16: No), when a single point of failure has been detected, that is,when there is a single point of failure (step S17: Yes), when thedistance of the stored additional route candidate the distance of thenewly stored additional route candidate is established, that is, whenthe newly stored additional route candidate is not the shortest amongthe additional route candidates (step S18: No), and after the process instep S19, the single point-of-failure detector 14 determines whetherthere is a single point of failure that has not been tried to be removedin step S14 in the previous processes (step S20). This is because thereis a case where a plurality of single points of failure exists on oneroute.

When there is a single point of failure that has not yet been tried tobe removed (step S20: Yes), the single point-of-failure detector 14returns to step S14 and generates the second topology informationobtained by removing the single point of failure that has not yet beentried to be removed, from the first topology information in the linkstate database 11 in step S14. The subsequent processes are as describedabove. In this manner, the single point-of-failure detector 14 decidesthe additional route on the basis of the additional route candidateinformation and generates the additional route information to registerin the forwarding database 13.

Furthermore, the single point-of-failure detector 14 decides thetransfer device 10 or the communication passage between the transferdevices 10 included in all the shortest routes in the redundant routeinformation as the single point of failure, and generates the secondtopology information obtained by removing one of the decided singlepoints of failure from the first topology information. When there is aplurality of single points of failure, the single point-of-failuredetector 14 generates the second topology information by changing thesingle point of failure to be removed.

When all the single points of failure have been tried to be removed(step S20: No), the single point-of-failure detector 14 generates theadditional route information with the additional route candidate storedby the process in step S19 as an additional route, and registers theadditional route information in the forwarding database 13 (step S21).When there is a plurality of additional route candidates linking thetransfer device 10 at the start point to the transfer device 10 at theend point, on which a single point of failure has not been detected, thesingle point-of-failure detector 14 decides an additional routecandidate having the shortest route length among the plurality ofadditional route candidates, as the additional route and generates theadditional route information. Steps S17 to S21 constitute a seconddetection step.

Note that, in the transfer device 10, the processes from step S13 tostep S20 may be carried out for a specific route designated by anadministrator of the mesh network 31 illustrated in FIG. 4, for example,the route from the transfer device 10-1 to the transfer device 10-11, ormay be carried out for routes between all the transfer devices 10constituting the mesh network 31.

Subsequently, hardware that implements the transfer device 10 will bedescribed. FIG. 8 is a diagram illustrating a hardware configurationexample of the transfer device 10 according to the present embodiment.The transfer device 10 can be implemented by a processor 91, a memory 92and data transfer hardware 93 illustrated in FIG. 8. The processor 91,the memory 92, and the data transfer hardware 93 mentioned above areconnected via a bus 94.

The processor 91 is a central processing unit (also referred to as CPU,processing unit, arithmetic unit, processor, microprocessor,microcomputer, or digital signal processor (DSP)), a system large scaleintegration (LSI), or the like. The memory 92 is a nonvolatile orvolatile semiconductor memory such as a random access memory (RAM), aread only memory (ROM), a flash memory, an erasable programmable readonly memory (EPROM), an electrically erasable programmable read onlymemory (EEPROM), a magnetic disk, a flexible disk, an optical disc, acompact disk, a mini disk, a digital versatile disc (DVD), or the like.

The link state database 11, the forwarding database 13, and the virtuallink state database 15 of the transfer device 10 are implemented by thememory 92. The redundant route calculator 12 and the singlepoint-of-failure detector 14 of the transfer device 10 are implementedby software, firmware, or a combination of software and firmware. Thesoftware and the firmware are described as programs and stored in thememory 92. The redundant route calculator 12 and the singlepoint-of-failure detector 14 are implemented by the processor 91 readingout programs for working as each of the redundant route calculator 12and the single point-of-failure detector 14 from the memory 92 andexecuting the read-out programs. That is, the transfer device 10includes the memory 92 for storing retaining a program that willeventually execute the steps for carrying out the actions of theredundant route calculator 12 and the single point-of-failure detector14 when the function of the transfer device 10 is executed by theprocessor 91. It can also be said that these programs are programs forcausing a computer to execute various processes performed by theredundant route calculator 12 and the single point-of-failure detector14.

The redundant route calculator 12 and the single point-of-failuredetector 14 may be implemented by dedicated hardware. FIG. 9 is adiagram illustrating another hardware configuration example of thetransfer device 10 according to the present embodiment. The redundantroute calculator 12 and the single point-of-failure detector 14 areimplemented by a processing circuit 95 as dedicated hardware. Asdedicated hardware, a single circuit, a composite circuit, a programmedprocessor, a parallel programmed processor, an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA), or acombination thereof are applicable. One of the redundant routecalculator 12 and the single point-of-failure detector 14 may beimplemented by dedicated hardware and the rest may be implemented by theprocessor 91 and the memory 92 described above.

The data transfer hardware 93 is used when the transfer device 10receives data from another transfer device 10 or the terminal device 20and when the received data is transferred to another transfer device 10or the terminal device 20. The data transfer hardware 93 is also usedwhen information to be stored in the link state database 11 is receivedfrom the outside.

As described thus far, according to the present embodiment, when asingle point of failure has been detected in a mesh network made up ofthe plurality of transfer devices 10, the transfer device 10 decides theadditional route on the basis of the second topology informationobtained by removing the single point of failure from the first topologyinformation on the mesh network, and stores the decided additional routetogether with information on the redundant route obtained from the firsttopology information. With this configuration, the transfer device 10can store information on a route not including a single point of failureand can improve the reliability of communication in the mesh network.

The configuration illustrated in the above embodiment indicates oneexample of the content of the present invention and can be combined withanother known technology. A part of the configuration can also beomitted and modified without departing from the gist of the presentinvention.

REFERENCE SIGNS LIST

10, 10-1 to 10-11 transfer device; 11 link state database; 12 redundantroute calculator; 121 shortest route calculator; 122 tie breaker; 13forwarding database; 14 single point-of-failure detector; 15 virtuallink state database; 20-1 to 20-7 terminal device; 30, 31, mesh network.

1. A transfer device comprising: a redundant route calculator to, on thebasis of first topology information that is topology information on anetwork made up of a plurality of transfer devices, calculate one ormore shortest routes from a first transfer device to a second transferdevice among the plurality of transfer devices, and generate redundantroute information that is information on the one or more shortestroutes; an information storage to store the redundant route information;and a single point-of-failure detector to detect a single point offailure on the basis of the redundant route information and generatesecond topology information that is topology information obtained byremoving the single point of failure from the first topologyinformation, wherein on the basis of the second topology information,the redundant route calculator calculates a candidate of an additionalroute to be added as a route from the first transfer device to thesecond transfer device, and generates additional route candidateinformation that is information on the candidate of the additionalroute, and the single point-of-failure detector decides the additionalroute on the basis of the additional route candidate information, andgenerates additional route information that is information on theadditional route, to register the generated additional route informationin the information storage.
 2. The transfer device according to claim 1,wherein the single point-of-failure detector decides a transfer deviceor a communication passage between the transfer devices included in allthe shortest routes in the redundant route information as the singlepoint of failure, and generates the second topology information obtainedby removing one of the decided single points of failure from the firsttopology information.
 3. The transfer device according to claim 2,wherein when there is a plurality of the single points of failure, thesingle point-of-failure detector generates the second topologyinformation by changing the single point of failure to be removed. 4.The transfer device according to claim 2, wherein when there is aplurality of additional route candidates on which a single point offailure has not been detected, the single point-of-failure detectorgenerates the additional route information with an additional routecandidate having the shortest route length among the plurality ofadditional route candidates, as the additional route.
 5. A routeaddition method comprising: a first calculation step in which, on thebasis of first topology information that is topology information on anetwork made up of a plurality of transfer devices, a redundant routecalculator calculates a plurality of shortest routes from a firsttransfer device to a second transfer device among the plurality oftransfer devices, and generates redundant route information that isinformation on the plurality of shortest routes, to register thegenerated redundant route information in an information storage; a firstdetection step in which a single point-of-failure detector detects asingle point of failure on the basis of the redundant route informationand generates second topology information that is topology informationobtained by removing the single point of failure from the first topologyinformation; a second calculation step in which, on the basis of thesecond topology information, the redundant route calculator calculates acandidate of an additional route to be added as a route from the firsttransfer device to the second transfer device, and generates additionalroute candidate information that is information on the candidate of theadditional route; and a second detection step in which the singlepoint-of-failure detector decides the additional route on the basis ofthe additional route candidate information, and generates additionalroute information that is information on the additional route, toregister the generated additional route information in the informationstorage.
 6. The transfer device according to claim 3, wherein when thereis a plurality of additional route candidates on which a single point offailure has not been detected, the single point-of-failure detectorgenerates the additional route information with an additional routecandidate having the shortest route length among the plurality ofadditional route candidates, as the additional route.